Purpose Insomnia is highly prevalent in people who are affected by cancer. However, options available to receive support for insomnia are limited. Telephone-based help services, such as cancer helplines, may be ideally placed to meet unmet needs regarding insomnia after cancer. The present study describes the prevalence and predictors of insomnia in patients and caregivers who call cancer helplines seeking support. Methods Participants (N=500 patients, N=234 caregivers) were recruited through an Australian state-based telephone-delivered cancer helpline. In addition to routine screening with the Distress Thermometer, participants were administered the Insomnia Severity Index. Results Most participants were female, older than 50 years of age, and were three (caregivers) to four (patients) months post-diagnosis. Insomnia symptoms were reported by 59.4 % of patients and 62.9 % of caregivers, with moderate to severe levels of insomnia reported by 27 % of patients and 30 % of caregivers. Insomnia was predicted by distress level for both patients (߽.31, p<.001) and caregivers (߽.32, p<.001) and age for patients only (߽-.13, p<.01). Conclusions Insomnia symptoms are common in patients and caregivers who call cancer helplines and appear to be related to distress. Telephone-based helplines have the potential to act as the first line of support in a stepped care approach addressing insomnia.